Microcapsules are spherical objects which consist of a core and a wall material surrounding the core, wherein the core in principal can be a solid, liquid or gaseous component which is surrounded by the solid wall material. For many applications the wall is formed by a polymer material. Microcapsules usually have a volume average diameter from 1 to 1000 μm.
A multitude of shell materials is known for producing the wall of microcapsules. The shell can consist either of natural, semisynthetic or synthetic materials. Natural shell materials are, for example, gum arabic, agar agar, agarose, maltodextrins, alginic acid or its salts, e.g. sodium alginate or calcium alginate, fats and fatty acids, cetyl alcohol, collagen, chitosan, lecithins, gelatin, albumin, shellac, polysaccharides, such as starch or dextran, polypeptides, protein hydrolyzates, sucrose and waxes. Semisynthetic shell materials are inter alia chemically modified celluloses, in particular cellulose esters and cellulose ethers, e.g. cellulose acetate, ethyl cellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose and carboxymethyl-cellulose, and also starch derivatives, in particular starch ethers and starch esters. Synthetic shell materials are, for example, polymers, such as polyacrylates, polyamides, polyvinyl alcohols, polyvinylpyrrolidones or polyureas.
Depending on the type of shell material and the production process, microcapsules are formed in each case with different properties, such as diameter, size distribution and physical and/or chemical properties.
Polyurea core-shell microcapsules obtained by reaction of at least one diisocyanate and at least one polyamine are well known in the art, for example from WO 2011/161229 or WO 2011/160733. According to WO 2011/161229 or WO 2011/160733 the polyurea microcapsules are prepared in presence of polyvinylpyrrolidone (PVP) as a protective colloid.
The development of biodegradable microcapsules was carried out mainly for drug transport and in-vivo release applications. Attention toward biodegradable capsules was increased since environmental aspects of polymers started to be discussed in the public and efforts were made to reduce environmental pollution.
Generally polyurethanes are prepared by reacting a polyisocyanate with a polyol component. Typical polyols employed in the preparation of polyurethanes are polyether polyols or polyester polyols. There is still a demand for polyurethanes that are suitable as polymeric shell material in microcapsules. For certain applications it would be advantageous that said shell material apart from having good application properties is also biodegradable.
WO 2006/044305 relates to an isocyanate-terminated prepolymer composition obtained by reaction of methylene diphenylisocyanate with a polycaprolactone polyol. The obtained prepolymer is used in the manufacture of polyurethane or polyurea elastomers.
WO 2008/033224 relates to isocyanate-terminated polycaprolactone polyurethane prepolymers obtained by reaction of toluene diisocyanate and a polyol composition. The obtained prepolymer can reacted with an amine chain extender resulting in polyurethane elastomers.
WO 03/061817 relates to substrates coated with polymers, containing microcapsules in the polymer layer, wherein the polymers includes for example polyurethanes, polyurethaneureas, polyacrylonitriles or copolymers of styrene.
U.S. Pat. No. 4,379,071 relates to a process for the production of microcapsules, wherein a diol or polyol which has a molecular weight of 400 to 10000 g/mol reacts with phosgene or a diisocyanate which contains at least two chloroformic acid esters or isocyanate groups per molecule. The resulting reaction product of those components is mixed with the desired core material and a chain lengthening agent which is at least bifunctional.
EP 0780154 relates to a process for preparing biodegradable microcapsules wherein the microcapsules are made by the addition reaction between polyamines, in particular aliphatic primary or secondary di- or polyamines, and polyisocyanate components containing at least one bifunctional isocyanate with an average of at least one ester and/or amide group in the main chain.
However, there continues to be a need for microcapsules, wherein the size of the micropasules can be controlled in a wide range and that are capable of releasing an encapsulated ingredient under controlled conditions. There is also a demand for microcapsules which have at least one encapsulated hydrophilic component, wherein the microcapsules have enhanced stability against leaking of the encapsulated components from the capsules. Delayed release of the encapsulated active ingredients for crop protection, personal care compositions or pharmaceutical compositions, is also of interest.